The invention discloses an open type isolation switch open/close state detection method and device; the method comprises the following steps: building an open type isolation switch finite element simulation model; calibrating and verifying the finite element simulation model; respectively selecting at least one most sensitive mechanical oscillation signal change point on the surface of an open type isolation switch support, an operating mechanism and a transmission system as the vibration measuring point positions; obtaining the corresponding relations between typical machinery faults and vibration signals; carrying out field vibration detection for the open type isolation switch with an unknown machinery state on the vibration measuring point positions of the open type isolation switch support, the operating mechanism and the transmission system, and estimating the corresponding machinery states according to a fault diagnosis classifier. The method and device can accurately detect the open type isolation switch open/close state without changing the structure, are high in safety and reliability, thus satisfying the field operation maintenance needs.